1. Field of The Invention
The present invention relates to the field of machine tools and more particularly to modifications ensuring exchange and storing of the tools of a high speed machine tool under the best conditions.
2. Discussion of the Background
High speed machining generally takes place from a tool rotatably driven by the motor driven axis of an electric spindle installed in a ram, which itself is mounted to be movable along three axis X, Y, Z.
A machine tool is classically provided with four main working stations, which are:
an actual machining station, comprising the tool driven rotationally by the motor driven axis of the electric spindle and shaping the workpiece to be machined. PA1 a training station situated upline from the machining station and made up of an ensemble of devices that ensure in particular the X, Y and Z movements of the ram of the electric spindle as well as the feed of the electric spindle for the rotation of its tool carrier axis, PA1 a control station cooperating with the drive station and functioning with a program of pre-established instructions to take charge of the different stages of machining of the said workpiece, PA1 a magazine for the storage of tools to keep the tools in use near the machining area, during the different stages of machining of the said workpiece. PA1 the machine to be used (milling machine, machine for turning . . . ) PA1 the different tools to use (milling tool, drill, threader . . . ) PA1 the displacements of the latter, PA1 the positionning of the workpiece with regards to the tool. PA1 a fixed chamber comprising an opening and associated with the frame of the machine tool, PA1 a cylinder revolving in the fixed chamber rotatably driven by a motor driven along an axis parallel to the axis of the ram and comprising a part for the storage of tools and another part for maintaining the seal of the fixed chamber. Thus the magazine, by the sole rotation movement of the cylinder, is able to: PA1 either provide the ram with an empty housing through the opening, PA1 or provide the ram with a housing comprising a tool placed in its tool carrier through the opening, PA1 or close, thus sealing the opening of its chamber in order to protect the container from all projections coming from the machining. PA1 a cylindrical part comprising peripheral gripping means of the tools placed at appropriated angular intervals, PA1 a part making a flap, integral with the cylinder and revolving with it, its profile and dimensions adapting to the profile and the dimensions of the said opening made in the fixed chamber in order to seal this chamber. PA1 a clamping device made up of two arms of which one end is pre-shaped to encircle the tool carriers in which the tools are housed on an axis parallel to the rotation axis of the cylinder, PA1 and of a semicircular cradle in line with the circle made up by the arms of the clamping device in which the tool carriers come into place.
The known device described and represented in patent FR-A-2 529 127 consists of a tool carrier carousel capable of revolving inside a chamber, which chamber is fitted with a revolving part enabling access to the spindle of the machine tool using such a magazine, to the tools and/or to the free machine tool areas. This device nevertheless has several disadvantages which make it useless in a high speed application where all stoppages or auxiliary delays must be reduced to a minimum if no eradicated. The opening of the fixed chamber is independent from the rotation of the carousel which implies an added time for functioning, but also an additional element (a motor). Furthermore, it is the rotation of the spindle which ensures the rotation of the carousel by a direct contact drive, it is therefore compulsory for the spindle to be in direct contact with the carousel to ensure its rotation, which implies an additional time delay as the magazine and the spindle need to be near one another before ensuring rotation of the carousel.
The classical machining of a workpiece is defined by a machining range comprising successive machining stages depending of the shape to give, and which define the following points:
The machining of a workpiece by a high speed machine tool depends on the machining program conceived by the department of machining engineering which decides on the machining stages during which different tools machine the workpiece according to a pre-established program.
This way of machining requires, near the machine tool, the presence of a tool magazine related to the ram of the machine tool to ensure storage of the tools to be used and their replacement when the machining stage of the machine is changed. Also, as some machining stages require the presence of tools of a large diameter, it is essential for the tool magazine to be able to store large size tools in order to provide for the wide variety of machine functions required by a workpiece.
A high speed machine tool must, by definition, ensure the quick exchange of tools in order to avoid a time delay affecting productivity. The aim of this magazine is therefore, to instantly provide the ram with a housing to enable the storage of the tool of the finished machining stage and a tool which will be used for the next machining stage according to the pre-established program.
The tools are fixed, each one in a tool carrier standard to all tools, and this tool carrier comes into place into the electric spindle fitted in the ram capable of receiving this type of tool carrier thus permitting the use of only one electric spindle. This tool carrier is provided with surfaces of reference ensuring the axial and radial positioning of the tool with regards to the electric spindle, these surfaces guarantee a referenced position of the tool, which is essential in all machining and particularly to the development of the program. A slight defect on these surfaces would result in a bad machining and therefore a bad workpiece or several bad workpieces if the defect was not quickly detected. Therefore, under no circumstances should these surfaces be bent or damaged by any impact or scratch. These surfaces need therefore protection against pollution resulting from machining i.e.: cuttings, oil projections and impacts, a protection difficult to implement in view of the proximity of the ram. Futhermore, should this protection start to fail and let cuttings in, it is very important that these do not build up in the place of storage for the tools.
Another disadvantage of the proximity of the ram, is the impossibility for an operator to have access to the tools in the magazine when the machine is functioning for obvious security reasons.
Taking this into account, the Applicant has carried out research with the aim of improving the storage device for tools of a machine tool, while avoiding the problems created by high speed machining.